Iran denied access to its airspace to a Bulgarian government jet taking a delegation led by Prime Minister Boyko Borissov to Tehran’s regional arch-enemy Saudi Arabia, prompting protests from Sofia, in an incident Tehran later blamed on a technical glitch, Sofia’s foreign minister said on Wednesday as quoted by Reuters.

Ekaterina Zaharieva told reporters the plane had all necessary permits to fly over Iran en route to Riyadh late on Tuesday but once it entered Iranian airspace it was asked by Iranian authorities to leave. The plane was also carrying former Bulgarian king Simeon Saxe-Coburg and four other cabinet ministers.

Zaharieva, part of the delegation on board, said the aircraft had to return to Turkey after what she called an “inexplicable last-moment refusal” by Iran. She said the plane had to get permission to fly through Iraqi airspace, to the west of Iran, before it could reach its final destination. She said Tehran had told Sofia the air access refusal was due to a slight deviation of the plane from its planned route, but Bulgarian authorities disagreed and had summoned the Iranian charge d‘affaires to Bulgaria for an explanation.

“The government aircraft had secured all the necessary diplomatic permissions to fly over Iranian airspace,” Zaharieva said.

The Iranian charge d‘affaires, Hassan Dotagi, said he deeply regretted the case and described it as a “technical misconception”, according to a Bulgarian Foreign Ministry statement following the meeting.

“The Bulgarian embassy provided the coordinates of the flight and we gave authorization, but the coordinates transmitted by the pilot to the control tower did not correspond with those which had been provided, so they refused the overflight. There was no political intention. We have even given permission for the return flight,” Iranian Foreign Ministry spokesman Bahram Ghasemi told AFP.

It was the first visit by a Bulgarian prime minister to Saudi Arabia since the former communist country, now a member of the European Union, and the kingdom established relations 20 years ago. Borisov was due to be received on Wednesday by Saudi King Salman and by the powerful Crown Prince Mohammed bin Salman, under whom relations with Iran have deteriorated dramatically. The Sunni Muslim kingdom of Saudi Arabia and Shi‘ite Muslim Iran support rival sides in wars and political crises throughout the Middle East.